How to clear all keys of all objects and bone?
Using scripts

Often for repetitive (&amp; tedious) tasks it is handy to use a small script.  

Remove all actions in file

Keyframed animation data is stored in an action. To completely remove all keyframed animation data, can remove all actions in the file.

import bpy
for a in bpy.data.actions:
    bpy.data.actions.remove(a)


Clear all animation data on scene and scene objects

To remove animation (actions, NLA, drivers) from scene objects and scene, but keep the actions in file.

import bpy
scene = bpy.context.scene
scene.animation_data_clear()
for o in scene.objects:
    o.animation_data_clear()